On each one of those wires, connected to that + bus bar, you (and I will soon also) have to start tracing back to where they go. Some of that will go directly to the battery, I suspect, as they did in my unit. 12v things like slides, levelers, etc still work after I cut power on the cutoff above. In fact in mine .. during inspection, I discovered that the cutoff didn't turn off anything. All 12v service was still alive, so there was no way to turn off 12v to work on a 12v circuit. I reported to the dealer, and he changed some of the wiring so that all but what is logically necessary (slides, levelers, Smoke/CO) would be able to be shut off .. but I didn't see what he did. I figured when I dig into it to install my MPII, I'd figure it all out. It's definately a discovery process and decision process on what to keep and what to change.
You go first and tell me what you learned